THE CAMBRIAN TO PERMO-TRIASSIC ARAFURA BASIN, NORTHERN AUSTRALIA

The Arafura Basin is on the northern margin of Australia, extending north towards New Guinea and contains a thick Cambrian to Permo-Triassic sedimentary sequence. The basin consists of a broad northern platform, a northwest trending graben, the Goulburn Graben (new name), and a southern platform that extends onshore into the Northern Territory. The basin sediments unconform- ably overlie the Proterozoic McArthur Basin and are overlain by mid-Jurassic and younger sediments of the Money Shoal Basin. The Palaeozoic section in the Goulburn Graben is over 10 km thick, while on the northern and southern platforms half that thickness is preserved. During the Cambrian and Ordovician the Arafura Basin was a stable platform dominated by carbonate deposition. The Late Devonian and Late Carboniferous aged sediments are marine and non-marine clastics with minor carbonates. Initial movement of the graben bounding faults occurred in the early Carboniferous, but the major graben development and deformation occurred in the Permo-Triassic and was associated with westward tilting. The six exploration wells in the basin have all been sited on structural targets along the Goulburn Graben. There were oil shows in most wells and four source rock intervals were intersected, but reservoir quality and fault seal were identified as major risks. The majority of the Cambrian and Permo-Triassic sequences remain untested and extensive areas of the basin outside the graben are virtually unexplored. Thermal maturation studies indicate a low geothermal gradient and that the greater part of the Palaeozoic sequence is prospective for hydrocarbons.